Wooden supports have many applications including supporting power lines, bridges, wharves, and buildings. The wooden supports are selected for use based on the load anticipated on the support. The size of the support, timber species, and treatment of the support are all important selection factors. While in service the supports may degrade and weaken due to a number of causes such as termite infestation and fungus attack. The deterioration of the wooden supports may be entirely internal and not visible on the outside of the support. Degradation in wooden supports is often unpredictable and the onset of loss of integrity in the support may not be related to time in service. Further to this some internal defects leave the wooden supports with sufficient strength that replacement of the support is unwarranted and wasteful. It is therefore desirable to provide a system and method that can assess the strength of the wooden support.
Current industry ‘best practice’ for determining deterioration in a wooden pole or support is to periodically drill into the wooden support to determine the annulus of the remaining sound wood. An average wall thickness for the wood support is then assumed. This method produces a high level of uncertainty due to both the variability of wood strength and the inherent errors in determining section properties. Further to this, drilling and plugging holes in wooden supports is undesirable.
Another device for measuring the extent of decay in a wooden support is an inspection probe that is inserted into an inspection hole drilled in a wooden support. One end of the probe includes a barb that engages with the side wall of the inspection hole and shears fibres from the inspection hole as the probe is withdrawn. The mechanical force needed to withdraw the probe from the inspection hole is measured with a pull-force over a certain value indicating a transition within the wooden support from decaying wood to sound wood. This device suffers from the same hole drilling and plugging problem as the current best practice described above.
A non-destructive method of estimating the residual strength of wooden supports uses portable computed tomography to image cross sections of the wooden supports. This method involves taking a plurality of gamma or x-ray attenuation measurements of the wooden support at varying locations around a 180 degree section of the wooden support. The attenuation measurements are then combined to provide a density image of the wooden support from which a strength estimate can be made. This method is reliable but is time consuming to take measurements with each wooden support measurement taking between ten and fifteen minutes.